1. Field of Invention
This invention relates to an improved high speed contact printing process for the duplication of information contained on a master tape onto a magnetic copy tape and, more particularly, to such a process wherein improved contact between the master and copy tapes is achieved through the application of fluid (typically air) pressure in accordance with the invention.
2. State of the Art
The prerecording of magnetic tapes generally may be accomplished in two ways. In the prevailing process, real time recording, a magnetic signal is read from a master recording and, after appropriate amplification and splitting, is recorded on the magnetic copy tape at the same speed that will be used in playing back the copy tape. This is substantially the same process that is used in home recording equipment, but up to one thousand recording machines are simultaneously operated from the signal generated by the master recording to bring the process to commercial scale. The logistics of providing, loading, unloading, operating and maintaining such a multitude of relatively complex equipment makes reproduction an expensive process.
In contact printing processes, in contrast, the copy tape is brought into physical contact with a master tape that bears the desired recording. The copy and master tapes are transported through a printing station where information contained on the master tape is duplicated onto the copy tape. The duplication technique may be anhysteretic, as generally described in High Speed Video Tape Duplication by Odagiri and Sato (IEEE Transactions, Aug., 1984), or thermomagnetic, as generally described by King in U.S. Pat.No. 4,213,159 and by Chouinard et al. in U.S. Pat.No. 4,631,602. In either case, copies are being made one-at-a-time and high speed duplication is essential if the process is to provide a practical alternative to the real-time technique generally used in preparing precorded video tapes.
As duplication speed increases, it becomes more difficult to maintain the precise registration and contact between the master and copy tapes that is needed for faithful duplication of the magnetic signal. Even microscopic slippage and/or separation between the tapes, which often occur simultaneously, will result in RF signal transfer deterioration, causing the copy tape to be of unacceptable quality.
Copending U.S. Pat.application Ser. No. 848,091, filed on Apr. 4, 1986, incorporated hereby by reference discloses a high speed thermomagnetic tape duplication process in which fluid pressure (typically compressed air) is employed to urge the master and copy tapes into close contact during the duplication step, and in which at least one of the tape surfaces that contacts the other has a specified roughness that facilitates the escape of air trapped between the two tapes as they are brought into contact. In this manner duplication speeds in excess of 2.5 meters/second may be obtained. However, it has been found that the master tape tends to become smooth in the course of thousands of recording cycles, due in part to buildup of lubricants driven from the copy tapes by heating, and RF signal transfer begins to deteriorate.
Japanese Patent Application 61-175931, published Aug. 7, 1986 discloses that tape slippage in an anhysteretic contact printing apparatus may be eliminated by providing an air jet and air collection channel with the channel extending at least from the jet toward the direction of tape travel (i.e., downstream). This approach was attempted in the process and equipment disclosed in the above-identified copending application, but there was no reduction in undesired tape slippage.